Wednesday, March 21, 2018

Why Nathan and I Aren't Related (Even Though We Are)

Despite having 30 years of concentrated family history research, we are always learning new tips and techniques. My latest tool is using DNA.

I first took a DNA test years ago mostly to prove to my Irish "cousins" that my Sherry line does not come from Ireland, but from Germany. My research was correct and the DNA proved that. And then the results sat for years.

In the past 3-4 months I have learned to do other comparisons including comparison tests across other companies. I have spent years documenting the Laumaster Project and I met two willing cousins to compare results.

In York, Pa., in the early 19th century, were four Laumaster/Lowmaster brothers. Jacob (1781); John (1783); George (1786); and Charles "Carl" (1791). I have been in contact with cousins on all lines except for Charles' line to test our relationships.

Our initial DNA comparison was with Cece DeBolt (John), Sharon Tomes (Jacob) and me (George). None of us matched.

We were all taken aback but as I said "every test is a clue" (not realizing at the time that I was right) and we needed to gather the results of more tests. Ancestry DNA showed I matched some people who claimed the Laumaster/Lowmaster tree. These included some closer one, Beth Lutes and Bill Seger, and some farther out, Gary Wilson and Daniel George. And there were some unknown ones with screen names including gatorsag17. All I could identify appeared to be from the line of George.

But searching on Laumaster in AncestryDNA I found that I match Christine Leavitt from Jacob's line. This is important because absent multiple lines, this shows I am related to Sharon's line from Jacob.

Every test is a clue and I kept looking. Finally, Nathan Lowmaster took a test. This, I thought, would be low hanging fruit. Nathan uploaded his results to GEDMatch and I did a comparison.

I was stunned. We were not related.

Nathan had emailed me when he was 12 looking for information on the Lowmaster family. After receiving permission from his dad to have the conversation, we kept in contact over the last 16-17 years. I know his line. Hie great-grandfather, Rev. E. A. Lowmaster, and my grandfather, William T. Lowmaster, were second cousins.

Rev. Lowmaster's dad was Oscar. He and my great-grandfather, Thomas Lowmaster, were cousins. In 1998, we stopped in Lewistown, Pa. and visited Oscar's son, David. The only visual I took from that day was seeing a photo of Oscar and thinking how much he looked like my grandpa's brothers. The family resemblance was strong.

Oscar and Jean Lowmaster
Credit: Christina Lowmaster Kensiger
And yet, this test. This test said we were not related. My head started spinning. Crazy thoughts about my own ancestry dashed through my head but the most serious was I thought about blowing up 30 years of research because I had it all wrong.

Every test is a clue. And there were clues in there. Nate matched my 3rd cousin, Bill Seger. But very strangely, he matched Cece Debolt from the line of John. That didn't make sense to me.

How could Nate be related to Cece (and I didn't match her), but not to me? This did not make sense.

I studied. I read. I tried to get my hands on everything related to DNA testing. And I figured it out.

First, Nathan IS related to me even though he isn't. He is my 4th cousin, once removed (his dad and I are 4th cousins) even though we don't share DNA (except we do).

To understand this we have to understand how DNA is measured. And that is in units called centimorgans (or cM). Since the human race is made up of DNA, on some level we all share some common DNA by luck. If we used the threshold of 1 or 2 we are related to tens of thousands, probably millions, of people.  Maybe to everybody.

The threshold units of centimorgans that testing companies use is seven. This generally eliminates showing test results that occur simply by luck. So Nathan and I do not share DNA at this threshold of sevens cMs. I was able to compare our DNA at 4.5 cM and we do share some DNA.

If I were to compare myself to the general population using 4.5 cMs as the threshold, there would be people I share with called "identical by luck." But Nathan and I do share some DNA not by luck. We are related.

I went into this thinking, and probably most readers do too, that if you are related you share DNA (above this threshold level of seven). And that is not the case.

First, if the DNA tests show you have common DNA, then you are related. Or most likely related. However, if the DNA tests do not show you have common DNA, it does not mean you are not related. Rather, it means you do not share common DNA above the seven centimorgan threshold.

This is true for more distant relationships. At first and second cousins, there is a 100% chance that cousins share some DNA. At 3rd cousins it is a 98% chance. And then it starts to drop.

At 4th cousins there is a 71% chance you share some DNA. So I could test against Nathan's dad Scott, a 4th cousin, and also in that line, Bill Lowmaster from Punxsutawney, his brother, Ben, and Christina Kensinger - all 4th cousins of mine. I should expect that three of those four I will share some DNA with but one of them I will not. We're still cousins - we just don't share some common DNA above the threshold level of seven cM.

At 5th cousins the chance of sharing DNA drops to 32%. So I suspect that being 4c1r, the chance of Nathan and I sharing DNA was about 50%. We may or we may not.

Cece and I are 5th cousins so we had a one in three chance of matching. It should not have come as a surprise when we did not match. But Nathan and her did match. They are 5c1r. At 6th cousins it drops to 11%. So they may have had a 20% chance of matching. And they did.

But assigning probabilities in this makes it much easier to see why Nathan and I did not match, even though we are cousins. The documentation remains vitally important. I'm not getting rid of 30 years of research. DNA can tell us who we are related to, but even if we don't match (probably at 4th cousins and distant), it does not mean we are not related, only that we don't share enough of the same DNA for one of these tests to show that we are. But we are.

Source: Crista Cowan, The Barefoot Genealogist